Inferred Conduit Network Geometry from Geological Evidences and Water-Head in a Fluvio-Karstic System (Val D’Orleans, France)

Flow modeling is a useful tool to investigate sustainable scenarios of water use for groundwater resources managers. However, the applications of this approach in karstic aquifers are still limited due to the difficulties of locating and describing the position and geometry of conduits. In the karstic aquifer of the ‘Val d’Orléans’ (France), the location of the conduits was identified by the presence of land-surface collapses and voids in the boreholes. In this dataset, 103 logs showed voids >0.1 m and a highly porous zone around 80 m.a.s.l. In this chapter, a methodology is proposed to interpolate the dataset to build a karstic network at the regional scale. Here, four scenarios of the conduit network geometry are tested, related to the morphology of the network and its complexity. The scenarios are included in a 3D coupled continuum-conduit flow model (Feflow®). The flows in the conduits and in the host rock are respectively described by the Manning-Strickler equation and Darcy’s law. Constant boundary conditions and hydrodynamic properties are assumed to test the model sensitivity to different network geometry scenarios. The most relevant scenario is selected by comparing calculated and observed water-heads in the boreholes. It aims to calculate a water balance at the regional scale, results suggest that accurate models (correlation coefficient r² > 0.9) can be obtained with an average hydraulic diameter approach and with highly simplified conduit network geometries. This confirms the interest of discrete continuum approaches, even if the actual conduit geometry will never be known.